visualizer vs beholder

visualizer and beholder both are nouns.

Word	Noun	Adjective	Verb	Adverb
visualizer	Yes	No	No	No
beholder	Yes	No	No	No

As nouns, beholder is a hypernym of visualizer; that is, beholder is a word with a broader meaning than visualizer:

visualizer: one whose prevailing mental imagery is visual
beholder: a person who becomes aware (of things or events) through the senses

Other hypernyms of visualizer include observer, perceiver, percipient.

visualizer (noun)	beholder (noun)
one whose prevailing mental imagery is visual	a person who becomes aware (of things or events) through the senses